In collecting butterflies and moths for cabinet specimens, one needs a gauze net a foot and a half deep, with the wire frame a foot in diameter; a wide-mouthed bottle containing a parcel of cyanide of potassium gummed on the side, in which to kill the moths, which should, as soon as life is extinct, be pinned in a cork-lined collecting box carried in the coat pocket. The captures should then be spread and dried on a grooved setting board, and a cabinet formed of cork-lined boxes or drawers; as a substitute for cork, frames with paper tightly stretched over them may be used, or the pith of corn-stalks or palm wood. Caterpillars should be preserved in spirits, or in glycerine with a little alcohol added. Some persons ingeniously empty the skins and inflate them over a flame so that they may be pinned by the side of the adult. Some of the most troublesome and noxious insects are found among the moths. I need only mention the canker worm and American tent caterpillar, and the various kinds of cut worms, as instances. [Illustration: 43. Parasite of the American Silk Worm.] We must not, however, forget the good done by insects. They undoubtedly tend by their attacks to prevent an undue growth of vegetation. The pruning done to a tree or herb by certain insects undoubtedly causes a more healthy growth of the branches and leaves, and ultimately a greater production fruit. Again, as pollen-bearers, insects are a most powerful agency in nature. It is undoubtedly the fact that the presence, of bees in orchards increases the fruit crop, and thus the thousands of moths (though injurious as caterpillars), wild bees and other insects, that seem to live without purpose, are really, though few realize it, among the best friends and allies of man. Moreover, insects are of great use as scavengers; such are the young or maggots of the house fly, the mosquitoes, and numerous other forms, that seem created only to vex us when in the winged state. Still a larger proportion of insects are directly beneficial from their habit of attacking injurious species, such as the ichneumons (Fig. 43, the ichneumon of the American silk worm) and certain flies (Fig. 44, Tachina); also many carnivorous species of wasps beetles and flies, dragon flies and Aphis lions (Fig. 45, the lace-winged fly; adult, larva and eggs). [Illustration: 44. Tachina, parasite of Colorado Potato Beetle.] [Illustration: 45. The Lace-winged Fly, Its Larva and Eggs.] But few, however, suspect how enormous are the losses to crops in this country entailed by the attacks of the injurious species. In Europe, the subject of applied entomology has always attracted a great deal of attention. Most sumptuous works, elegant quartos prepared by naturalists known the world over, and published at government expense, together with smaller treatises, have frequently appeared; while the subject is taught in the numerous agricultural colleges and schools, especially of Germany.